The present invention relates to a conduction control device.
New types of electronic devices are emerging in which carrier transport is controlled, at least in part, by charge carrier spin. Well-known examples of these so-called “spintronic” devices include spin valves, based on the giant magnetoresistive effect (GMR), and magnetic tunnel junction (MTJ) devices. Generally, these devices comprise alternating layers of ferromagnetic and non-ferromagnetic material, the non-ferromagnetic material being metallic (in the case of a spin-valve) or insulating (in the case of MTJ device). Spintronic devices have several applications, including magnetic field sensors and magnetic random access memory (MRAM). A review of spin-based electronics and applications is given “Spintronics: A Spin-based Electronics Vision for the Future” by S. A. Wolf et al., Science, volume 294, pp. 1488 to 1495 (2001).
In early spintronic devices, the ferromagnetic material usually comprised a metal, such as iron (Fe), cobalt (Co) or nickel (Ni), or an alloy thereof. However, some, more recent spintronic devices use a ferromagnetic semiconductor, such as gallium manganese arsenide (Ga,Mn)As, which is described in “Making Nonmagnetic Semiconductors Ferromagnetic” by H. Ohno, Science, volume 281, pp. 951 to 956 (1998).
Devices based on ferromagnetic semiconductors have demonstrated strong magnetoresistance effects.
For example, “Very Large Magnetoresistance in Lateral Ferromagnetic (Ga,Mn)As Wires with Nanoconstrictions” by C. Ruster et al., Physical Review Letters, volume 91, p 216602 (2003) describes a structure exhibiting tunnelling magnetoresistance (TMR). The structure is fabricated from a 19 nm-thick layer of Ga0.976Mn0.024As grown on semi-insulating GaAs, which is laterally defined by etching so as to form an island connected to wires on either side by narrow constrictions.
“Tunneling Anisotropic Magnetoresistance: A spin-value like tunnel magnetoresistance using a single magnetic layer” by C. Gould et al., Physical Review Letters, volume 93, p 117203 (2004) describes a device showing spin-valve like effects. The device comprises a pillar consisting of a titanium/gold (Ti/Au) metal contact on an aluminium oxide (AlOx) tunnel barrier disposed on a 70-nm thick layer of Ga0.94Mn0.06As grown on semi-insulating GaAs. The strong anisotropic hysteretic effect in this experimental device can be attributed to tunneling anisotropic magnetoresistance (TAMR) which results from strong spin-orbit coupling in a single ferromagnetic layer.